xfs: fix directory readahead offset off-by-one
PATCH 1/1 xfs: fix directory readahead offset off-by-one
From: Dave Chinner <[email protected]>
Directory readahead can throw loud scary but harmless warnings when multiblock directories are in use a specific pattern of discontiguous blocks are found in the directory. That is, if a hole follows a discontiguous block, it will throw a warning like:
XFS (dm-1): xfs_da_do_buf: bno 637 dir: inode 34363923462
XFS (dm-1): [00] br_startoff 637 br_startblock 1917954575 br_blockcount 1 br_state 0 XFS (dm-1): [01] br_startoff 638 br_startblock -2 br_blockcount 1 br_state 0
And dump a stack trace.
This is because the readahead offset increment loop does a double increment of the block index - it does an increment for the loop iteration as well as increase the loop counter by the number of blocks in the extent. As a result, the readahead offset does not get incremented correctly for discontiguous blocks and hence can ask for readahead of a directory block from an offset part way through a directory block. If that directory block is followed by a hole, it will trigger a mapping warning like the above.
The bad readahead will be ignored, though, because the main directory block read loop uses the correct mapping offsets rather than the readahead offset and so will ignore the bad readahead altogether.
Fix the warning by ensuring that the readahead offset is correctly incremented.
--- fs/xfs/xfs_dir2_readdir.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
fs/xfs/xfs_dir2_readdir.c +1 -1
@@ -456,7 +456,7 @@ xfs_dir2_leaf_readbuf(/* * Advance offset through the mapping table. */ -for (j =0 ; j < mp->m_dirblkfsbs; j++) { +for (j =0 ; j < mp->m_dirblkfsbs; ) {/* * The rest of this extent but not more than a dir * block.
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Quoted 13 lines · Dave Chinner
Fix the warning by ensuring that the readahead offset is correctly incremented.
Signed-off-by Dave Chinner <[email protected]>--- fs/xfs/xfs_dir2_readdir.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)fs/xfs/xfs_dir2_readdir.c +0
-0
fs/xfs/xfs_dir2_readdir.c xfs_dir2_leaf_readbuf( · line 462
Quoted 8 lines
fs/xfs/xfs_dir2_readdir.c +1
-1@@ -456,7 +456,7 @@ xfs_dir2_leaf_readbuf(/* * Advance offset through the mapping table. */ -for (j =0 ; j < mp->m_dirblkfsbs; j++) { +for (j =0 ; j < mp->m_dirblkfsbs; ) {/* * The rest of this extent but not more than a dir * block.
This looks correct, but it would seem a little more idiomatic to write this as:
for (j = 0; j < mp->m_dirblkfsbs; j += length) {and remove the j increment from the body.
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Quoted 26 lines · Christoph Hellwig
Quoted 13 lines · Dave Chinner
Fix the warning by ensuring that the readahead offset is correctly incremented.
Signed-off-by Dave Chinner <[email protected]>--- fs/xfs/xfs_dir2_readdir.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)fs/xfs/xfs_dir2_readdir.c +0
-0fs/xfs/xfs_dir2_readdir.c xfs_dir2_leaf_readbuf( · line 462
Quoted 8 lines
fs/xfs/xfs_dir2_readdir.c +1
-1@@ -456,7 +456,7 @@ xfs_dir2_leaf_readbuf(/* * Advance offset through the mapping table. */ -for (j =0 ; j < mp->m_dirblkfsbs; j++) { +for (j =0 ; j < mp->m_dirblkfsbs; ) {/* * The rest of this extent but not more than a dir * block. This looks correct, but it would seem a little more idiomatic to write this as:
Quoted 3 lines
for (j = 0; j < mp->m_dirblkfsbs; j += length) {and remove the j increment from the body.
yeah, I can do that.
Cheers,
Dave.
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Dave Chinner [email protected] _______________________________________________ xfs mailing list [email protected] http://oss.sgi.com/mailman/listinfo/xfs
Christoph Hellwig
Reviewed-byQuoted 1 line · Dave Chinner
yeah, I can do that.
with that.
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